The Toxicity of plant material , Drimia Altissima ( Urginea Altissima ) , Against the Field Rat , Arvicanthis Abyssinicus : A potential non - synthetic rodenticide

Background: Rodents are important pests of public health and agricultural importance, capable of transmitting diseases to humans and causing crop damage. The present rodent control strategy depends primarily on synthetic rodenticides, which are highly toxic, affect non-target species, and are expensive. Naturally produced organic pesticides may be more desirable as they are less toxic to non-target animals and are economically sustainable. Objective: The objective of the study is to explore the toxicity and palatability of the bulbs of Drimia altissima against the field rat, Arvicanthis abyssincus with the aim of developing locally based organic rodenticides. Method: This is a laboratory study for evaluating the toxicity of D. altissimia bait against the field rat, Arvicanthis abyssincus. In the study, field rats were randomly assigned to treatment and control groups. The treatment groups received different concentrations of D. altissimia poison bait prepared in the lab. The control groups received the plain bait. Mortality was recorded during the test period. Results: Of the treatment groups, 80%-100% of the rats receiving the poison bait died, while none of the rats offered a choice between the plain bait and the poisoned bait died. It is estimated that 8% of the powdered bulb would produce 50% mortality. Conclusion: The powdered bulb of D. altissima resulted in rat mortality in the test but not in the control group. The liberation of the toxic substance from the poisoned bait might have been slowed by the presence of the plain bait in the choice test. The result of this study suggests that further work is needed for understanding the toxicological properties of the active agents in the bulb. [Ethiop. J. Health Dev. 2010;24(3):175-179] Introduction Agricultural pests and zoonotic diseases are among the factors responsible for the chronic food shortages and for the high mortality rates from infectious diseases. In Ethiopia, the agriculture sector rodent depredations are a matter of concern in grain, fruit, and vegetable crops, as well as in reforestation projects (1). The unstripped grass rat, Arvicanthis abyssinicus, is the most widely distributed and economically important rodent pest in Ethiopia. This species is well adapted to live in areas inhabited by humans and is commonly found in open fields close to villages. It is a major pest of agricultural and public health significance. In Ethiopia, although data showing the level of crop loss due to rodents is lacking, in some areas it could reach as high as 10-25% during outbreak season (2). Rodents caused disease outbreaks, some like plague with historical significance, have been well documented in many countries (3). However, due to the lack of resources, underdeveloped human capacity and infrastructure, rodent caused diseases have not been documented in Ethiopia (2). In order to decrease rodent caused crop losses, government sponsored rodent control programs are carried out during outbreak seasons. The control strategy includes trapping, habitat alteration, and poisoning using zinc-phosphide and anticoagulant rodenticides (2). However, these rodenticides pose significant threat both to the environment and to public health. Acute poisonings with pesticides including rodenticides account for 300,000 death worldwide (4). Zinc-phosphide releases phosphine gas, which is a nervous system toxicant. Inhalation of phosphine gas released from inorganic phosphides used as fumigants was responsible for a death of a 6 year old boy and for two adults suffering from severe toxicity (5). In addition zinc phosphide is toxic to non-target animals including wildlife (6). Ingested zinc phosphide was found in carcasses of poisoned rodents and animals eating these carcasses might be at risk of secondary poisoning (7). In additional to zinc-phosphide, 1-generation anticoagulant rodenticides have also been used in rodent management program in Ethiopia. Compared to zincphosphide, anticoagulant rodenticides require multiple feeding, and as a result are less toxic to humans as well as to non-target animals. Furthermore, vitamin K can be used as antidote in case of accidental poisoning with anticoagulants. However, many rodent species have developed resistance to 1 generation anticoagulants (8) Ethiop. J. Health Dev. 176 Ethiop. J. Health Dev. 2010;24(3) and they are no longer used in rodent management program in Ethiopia (9). 2nd-generation anticoagulants were introduced in Ethiopia in recent years, but they still have environmental limitations. Like zinc phosphide, 2 generation anticoagulants are single-feed rodenticides, and as a result are potentially hazardous to non-target animals (10, 11). Furthermore, rats have developed resistance to 2 generation anticoagulants (12, 13). Therefore, due to their high cost, environmental limitations and resistance, the use of 2 generation anticoagulants has been curtailed in Ethiopia (2). Globally, there is a great deal of interest in developing and using naturally occurring plant-based chemicals for the management of pests of public health and agricultural importance. The added benefit of using naturally occurring pesticides is that they are sustainable, economically viable, and environmentally friendly. There are many native plant species in Africa with known chemical toxicity to animals that can be developed as pesticides. In the high land region of Ethiopia, farmers have been using the bulbs of a plant known as D. altissima for controlling rats (2). Bulbs of D. altissima contain acute cardiac glycosides known as bufadienolides (14), which affect primarily the cardiac system, but also affect the gastro-intestinal, respiratory, and nervous systems (15). Livestock poisoning in southern Africa has been linked to the consumption of the bulbs of D. altissimia during the dry season (15). The bufadienolides are typically polyhydroxy C-24 steroids with a pentadienolide ring at C-17, and have been extracted from bulbs of D. altissima in Ethiopia (16) and from a related species in South Africa (17). A preliminary study was conducted to evaluate the toxic effect of D. altissima against the field rat, A. abyssinicus, in a non-choice test. Exposures to 20% concentration of D. altissima preparation resulted in complete mortality of the test animals (2). So far there is no published study showing the toxicity of bulbs of D. altissimia against rodent pests. The purpose of the current study was to determine the rodenticidal properties (toxicity and palatability) of D. altissima preparation against the field rat, A. abyssinicus in a choice and non-choice tests. Methods The test rats were collected from pastoral lands and agricultural fields using live traps baited with bread spread with peanut butter. In the lab, the rats were kept individually in a metal cage measuring 37cm x33cm x21cm and maintained on a diet of whole wheat pellets and water ad libitum. After three weeks of acclimatization, each rat was sexed, weighed and returned to the cage for the test. Pregnant females, rats appearing sick and juveniles were excluded. The remaining rats were then randomly assigned into treatment and control groups. The treatment groups were divided into a choice and no-choice test groups. In the choice test the rats were given a choice between untreated and treated baits. In the non-choice test while the rats were given only the treated bait; the control rats were given the untreated bait. Bulbs cut from D. altissima were chopped into small pieces, allowed to soak in water for 24 hours and then washed. The chopped bulbs were immersed for a short time in 98% ethanol heated on a steam bath and afterwards air dried. The dried bulbs were crushed and ground in an electrical grinder until a powdery form of the material was produced. The test baits were prepared by mixing measured amounts of the powdered bulbs into a base containing 90% wheat flour, 5% vegetable oil, and 5% sugar. In this manner, treated baits containing 20%, 10%, 5%, and 0% of the powdered bulbs were prepared and offered to the rats in a choice and non-choice situation. In all test groups, 10 animals, 5 males and 5 females were used per dosage level. In the no-choice test, each animal received 20 grams of the treated bait ad libitum for 2 days , while in the choice test, each animal received 20 grams of the treated bait and 20 grams of the untreated (plain) bait water ad libitum in separate bowls. The positions of the bowls were alternated daily to avoid feeding position bias. The duration of the choice test was 4 days. The duration of the no choice test was 2 days. Ten rats of (5 males and 5 females) were used as control and were given 20 grams of the untreated bait water ad libitum for 4 days. In acute toxicity test animals are normally exposed to poison baits for a period of 1 to 2 days (18). However, in this case since this plant material has never been evaluated for its rodenticidal properties, we decided to extend the duration of the non-choice and the choice test to 2, and 4 days respectively. The rats were observed daily for the duration of the test period. In the control group the rats were observed only for signs of illnesses and the amount of the untreated bait they consumed was not recorded. The amount of baits consumed and the mortality patterns were recorded daily for the duration of the experimental period. The amount of bait consumed was calculated after adjusting for spilled food and for variation in daily moisture content. Each day, unspoiled single use paper towel was placed under each cage to facilitate the collection of spilled foods. Any spilled food would be carefully separated from feces, weighed and added to the unconsumed bait weight. The variation in bait weight due to moisture was determined by placing in separate cages 20 grams each of the treated and untreated baits under a similar laboratory condition and determining if there were daily variations in weight. Results None of the control animals died during the test period. They appeared healthy and were actively moving inside their cages. The exact amount of the untreated bait each control animal consumed was not recorded, but was visually estimated at approximately 50% or more of the original amount presented. There was no daily variation 177 The Toxicity of plant material, Drimia Altissima Against the Field Rat, Arvicanthis Abyssinicus Ethiop. J. Health Dev. 2010;24(3) in laboratory temperature and humidity. There was no gain or loss in weight due to moisture variation. There was no bait spillage during the test period. The exposure and mortality results are presented in Table 1. None of the animals that had a choice between plain food and food with the bulb mixture died. Table 1: Experimental Data Results Treatme nt Gende r N Mean body mass (g) Test Duration (day) % powdered bulb in Bait Mean daily bait intake (g) Dose (mg/kg/da y) Mean plain food intake (g) Powdered bulb (%) in total daily food intake Mortality (%) Choice Male 5 68.09 4 0 0 0 nr 0 0 5 82.6 4 5 0.42 254 5.34 0.4 0 5 85.1 4 10 0.34 400 6.61 0.5 0 5 89.23 4 20 0.42 941 7.27 1.1 0 Femal e 5 54.22 4 0 0 0 nr 0 0 5 79.33 4 5 0.4 252 6.87 0.3 0 5 97.03 4 10 0.42 552 7.59 0.4 0 5 76.63 4 20 0.4 1044 7.06 1.1 0 No Choice Male 5 78.16 2 0 0 0 nr 0 0 5 90.95 2 5 0.61 335 0 5 100 5 87.88 2 10 0.65 740 0 10 80 5 86.37 2 20 0.79 1829 0 20 100 Femal e 5 72.08 2 0 0 0 nr 0 0 5 58.04 2 5 0.57 491 0 5 100 5 60.48 2 10 0.64 1058 0 10 100 5 75.9 2 20 0.57 1502 0 20 40